Idle channel noise is a factor and consideration which often must be addressed in designing circuit configurations subject to required specifications. The use of an analog-to-digital (A/D) converter in a circuit containing idle channel noise will effectively convert the channel noise to a digital signal. If the signal passes through multiple A/D and D/A converters, then the noise may accumulate to an undesirable level.
In commercial telephone systems, the range of pertinent signal levels typically extends down to approximately -50 dBm. However, the idle channel noise within the system typically measures -80 dBm under c-message weighting. Under current telephone systems, the idle channel noise is permitted to remain in the signal. Accordingly, at idle time periods, the A/D converter will still output signals from -50 to -80 dBm representing noise.
The idle noise signal may violate a specification standard or requirement. Cumulative effects associated with the noise signal may also occur, thereby creating troublesome static on the line. Further, when the line is monitored by delicate digital equipment, the noise signal may have a deleterious effect thereon. Therefore, it is clear that the idle noise signal is undersirable. As a result, there exists a need for a method and apparatus for reducing noise having magnitudes less than -50 to -60 dBm.